1. Field of the Invention
The invention relates to an exhaust gas recirculation device with pressure compensation.
2. Description of the Related Art
Spark-ignition and diesel engines, especially those in motor vehicles, are usually provided with exhaust gas recirculation devices, especially exhaust gas recirculation valves (EGR valves). By means of the latter, exhaust gas is to some extent mixed with the fresh gas taken in, in order to reduce the NOx emission and to improve the fuel consumption, and to reduce the production of noise.
Such exhaust gas recirculation devices comprise metering means or control means with which the quantity of exhaust gas recycled can be set as a function of the operating point. Too little exhaust gas recirculation would not achieve the desired effects, too high exhaust gas recirculation in spark-ignition engines would lead to disruption of the operation or to an undesired rise in HC or even CO emissions and, in the case of diesel engines, would lead to an undesired increase in the particulate emissions.
Such control means are generally valves which can be closed completely and which are set by a vacuum diaphragm or an actuating motor or a proportional magnet operating counter to a spring, said means in turn being actuated by the controller of the engine via a cycling valve or a relay. The information used for this purpose in the controller is generally that relating to the load and rotational speed of the engine and to the quantity of air taken in. In order to improve the operation, use is also made of the feedback of the opening travel via a distance-measuring system.
The exhaust gas recirculation devices are located between the fluctuating pressures in the exhaust gas system and the fluctuation pressures in the intake system of the engine, the changes in these pressures on the one hand being associated with the changes in the operating point, and on the other hand being determined by the surge-like emergence of the exhaust gas and from the surge-like intake of the fresh air.
These pressure fluctuations constitute a problem for the metering function of the exhaust gas recirculation device in normally-aspirated engines, and are particularly serious in supercharged engines.
JP 06 147 025 (Patent Abstracts of Japan) shows an exhaust gas recirculation device such as is described in the preamble of claim 1. In this case exhaust gas from an internal combustion engine is fed to a dual valve via two exhaust gas feeds. The dual valve comprises two valve disks which are rigidly fixed to a valve rod and which in each case separate the exhaust gas feeds from a common exhaust gas recirculation duct, it being necessary for one valve disk to be moved in order to open the valve along the exhaust gas flow direction and for the other valve disk to be moved in the direction opposite the exhaust gas flow direction.
The object of the invention is to provide an exhaust gas recirculation device in which the quantity of exhaust gas which is passed through or metered is as far as possible independent of the above pressure fluctuations acting on the exhaust gas recirculation device.